1. Field of the Invention
The present invention relates to an X-ray diagnosis apparatus which diagnoses an object based on an X-ray diagnostic image of the object.
2. Description of the Related Art
An X-ray diagnosis apparatus which picks up a fluoroscopic image of a human body using X-rays or the like is known. This X-ray diagnosis apparatus is used to conduct angiography tests to observe the statuses of blood vessels in which a contrast medium has been injected. In the angiography tests, when an angiogram of a lower limb is taken, blood flows in a wide range should be traced in some case. In this case, a table moving pick-up scheme or the like is employed in which the X-ray tube and image intensifier system (hereinafter called "X-ray pick-up system") and an object are moved relative to each other to obtain angiograms.
FIG. 1 is a diagram showing the schematic structure of a conventional X-ray diagnosis apparatus. An X-ray tube 1 irradiates X-rays to an object 17 under the control of an X-ray controller 2. An image intensifier 5 converts X-rays passing through the object 17 into an optical image. A pick-up unit 6 (which is constituted of a CCD, for example) converts this optical image into a TV video signal, which is further converted into a digital signal by an A/D converter 7. The digital image signal is temporarily stored in an image memory 8, and is later output to an image processing unit 13 at a given timing. Digital image data which has undergone image adjustment processing in the image processing unit 13 is converted into a TV video signal by a D/A converter 14 and is displayed by an image display unit 15.
A supporter driving unit 18 moves a supporter 16 on which an X-ray pick-up system including the X-ray tube 1, image intensifier 5 and pick-up unit 6 (the supporter may hereinafter be simply called "X-ray pick-up system" sometimes) at a given speed in a predetermined direction. A bed driving unit 19 moves a bed at a given speed in a predetermined direction. A bed/supporter drive controller 20 controls the driving of the supporter driving unit 18 and the bed driving unit 19.
A description will be given of the occurrence of blurring of fluoroscopic images when the X-ray pick-up system (supporter 16) and the object 17 in the above structure moves relative to each other.
The table moving pick-up is executed while the bed driving unit 19 is driving the bed in response to a signal from the bed/supporter drive controller 20 during the irradiation of X-rays.
FIG. 2 shows the timing relation between an X-ray pulse and a collection image at the time of the conventional image collection.
The conventional X-ray diagnosis apparatus obtains a single X-ray fluoroscopic/pick-up image of an object (hereinafter simply called "X-ray diagnostic image") through a single irradiation. As shown in FIG. 2, a predetermined time T is needed as the time for a single irradiation (i.e., pulse width) to obtain a single X-ray diagnostic image. That is, an X-ray diagnostic image F.sub.1 is obtained through irradiation at time t.sub.1 and an X-ray diagnostic image F.sub.2 is obtained through irradiation at time t.sub.2. In this manner, a single X-ray diagnostic image F.sub.1, F.sub.2, F.sub.3, . . . of the object is obtained through every irradiation. In this case, when the supporter 16 and the bed 4 move relative to each other (e.g., the bed 4 moves while the supporter 16 is fixed) during the time T equivalent to the X-ray pulse width, passed X-rays which include the movement of the object 17 due to the movement of the bed 4 are input to the image intensifier 5. As the resultant X-ray diagnostic image gradually shifts in accordance with the movement of the bed 4 during the irradiation of X-rays, blurring occurs in the obtained X-ray diagnostic image. This blurring is of the same type as the image blurring that occurs in the ordinary visible-rays based photographing due to the shaking of a camera.
The following methods may be employed to prevent the blurring of an X-ray diagnostic image from occurring due to the relative movement of the supporter 16 to the object 17.
The first method is to narrow the X-ray pulse width (i.e., to shorten the time T as much as possible). Simply narrowing the X-ray pulse width results in an insufficient dose of X-rays so that an image having the desired brightness and contrast cannot be obtained.
In this respect, the amplitude of the X-ray pulse (i.e., the amount of X-ray irradiation) is increased or the sensitivity of the X-ray detector is enhanced while making the X-ray pulse width narrower. Further, the image processing method may be improved. Since there are limits to the performance of the X-ray generator and/or the performance of the X-ray detector or the like, however, it is difficult to employ those methods.
As mentioned above, conventionally, when the X-ray pick-up system and the object move relative to each other, passed X-rays which include their relative movement are input to the image intensifier, thus causing the blurring of the resultant X-ray diagnostic image.
To reduce the dose of the X-ray irradiation for the X-ray fluoroscopy, the above-described X-ray diagnosis apparatus is normally combined with a digital fluorography device (hereinafter called "DF device") which can record images.
The DF device converts an X-ray diagnostic image obtained through the sequential irradiation of X-rays into image data consisting of digital signals to perform various image processes, and has advantages such that blood vessels with a low density can be displayed clearly and quantitative diagnosis is possible.
One of the image processes of the DF device performs is the automatic adjustment of the brightness and contrast of an image. This function is to temporarily input one frame of image data into a (frame) memory and automatically adjust the brightness and contrast or the like based on the image data within an area of interest (concerning area) designated by an operator or the like.
FIG. 3 shows one example of an X-ray diagnosis apparatus which employs such a DF device. Like or same reference numerals are used in FIG. 3 to denote components corresponding or identical to those shown in FIG. 1 and their detained descriptions will not be given again.
X-rays irradiated from the X-ray tube 1 pass through the object 17 and enter the image intensifier 5 where the X-rays are converted to optical image data. An X-ray limiter 3 adjusts the X-ray irradiation field.
The output data of the image intensifier 5 is converted into a TV video signal by the pick-up unit 6, which comprises a camera tube, solid state pick-up element or the like, and this TV video signal is further converted to digital image data by the A/D converter 7. The digital image data is output via the memory 8 to an adjustment coefficient calculation unit 21, which computes image adjustment coefficients, and the image processing unit 13, which executes image processing.
The output data of the A/D converter 7, which is temporarily stored in the memory 8, is read out together with data of a concerning area designated by the operator or the like, output from a concerning area designating unit 22, from the memory 8 by the adjustment coefficient calculation unit 21. This adjustment coefficient calculation unit 21 computes adjustment coefficients for the brightness and contrast of an image, for example, based on the image data corresponding to the designated concerning area, and outputs the adjustment coefficients to the image processing unit 13.
The image processing unit 13 has a memory 13a, an image processing circuit 13b and an image adjustment circuit 13c. The memory 13a temporarily stores the output data of the A/D converter 7. The image adjustment circuit 13c reads the image data, held in the memory 13a, via the image processing circuit 13b and performs the adjustment of the brightness and contrast on the read image data using the adjustment coefficients output from the adjustment coefficient calculation unit 21. The image data that has undergone the image adjustment is converted to a TV video signal by the D/A converter 14 and is then sent to the image display unit 15.
Using the adjustment coefficients obtained from the image data within the concerning area of the (N-1)-th frame image data, the image adjustment circuit 13c automatically performs an image adjustment process on the (N-1)-th frame of image data or the self image. The processed image data is thus sequentially displayed as an X-ray diagnostic image frame by frame by the image display unit 15.
If there is no memory 13a in FIG. 3, while the data flow is the same as the one described above, the image adjustment circuit 13c automatically performs an image adjustment on the N-th frame based on the image data within the concerning area of the (N-1)-th frame, using the adjustment coefficients which optimize the image within that concerning area.
The above-described conventional X-ray diagnosis apparatus has the memory 13a in the image processing unit 13 to determine adjustment coefficients using the memory 8 and the adjustment coefficient calculation unit 21 and perform an adjustment process on the image on which the adjustment coefficients have been determined (i.e., self image). Therefore, the fluoroscopic image displayed on the image display unit 15 is delayed by one frame from the fluoroscopic image that is collected at that point of time. When the operator inserts, for example, a catheter into a body while viewing the X-ray diagnostic image, the difference between the image of the actual manipulation and the displayed X-ray diagnostic image often gives awkward manipulation feeling to the operator.
If the memory 13a is eliminated to overcome the above problem, the memory 8 and the adjustment coefficient calculation unit 21 are used to calculate adjustment coefficients which optimize the (N-1)-th image based on the image data within the concerning area of the (N-1)-th frame and the actual image adjustment is executed on the N-th image. With this method, however, the brightness and contrast are inadequately adjusted when there are large changes in brightness and contrast between the images within the concerning areas of the (N-1)-th frame and the N-th frame particularly in the case where X-ray irradiation field is moved, for example, in the direction along the axis of the object 17 in response to drive signals from the supporter driving unit 18 that drives the supporter 16 on which the X-ray tube 1 and image intensifier 5 are mounted the and bed driving unit 19 that drives the bed 4.
Although the difference between the displayed X-ray diagnostic image and the image of the actual manipulation and the inadequate image adjustment are overcome if the image adjustment is not performed, the brightness/contrast of the X-ray diagnostic image is not adjusted, so that visibility and diagnosis may be affected.